Bleeding and burning damage are actually defined the weapon.txt. Regarding scaling the effect, that is an issue. I'm not sure how exactly you want to scale it (by weapon damage I assume), but that will definitely take some clever thinking. Scaling it by a stat would be possible if you took a measure of the character's dexterity, for example (CharacterGetStat), and then apply a stronger version of the super-bleed effect depending on your dexterity (that is, you'd make like 5 different massive bleeding statuses with different damage totals). One interesting idea would be to scale it based on how many points in the nasty deeds stat you have. Every 3 points in Sneak, lockpicking or pickpocket would get you a stronger bleed effect.
I would think damage range would basically increase the variability of the damage by X percentage, with 10 being like 90-110, and 30 being 70-140 or something, but I haven't looked into it that much. I tend to prefer lower variability in that respect.